1. Field of the Invention
The present invention relates to a semiconductor device manufacturing technique and, more particularly, to a technique which is advantageous when used for manufacturing semiconductor devices incorporating power supply transistors such as power MOSFETs, IGBTs (insulated gate bipolar transistors) and bipolar power transistors, i.e., for manufacturing low voltage drive power transistors through reduction of electrical resistance used in the power supplies of portable apparatuses and the like, power transistors having low thermal resistance used in the power supplies of high output apparatuses such as laser beam printers and the like and power transistors for high current used in automobile electronics.
2. Description of the Related Art
Known power supply transistors incorporated in chargers for portable telephones, video cameras and the like and in power supply circuits of office automation (OA) apparatuses and the like include low voltage drive power transistors through reduction of an on resistance (Ron). For example, a power transistor for driving at a low voltage is described in xe2x80x9cHitachi Databook: Hitachi Semiconductor Packagexe2x80x9d issued in July, 1997 by Semiconductor Division, Hitachi, Ltd., page 329.
This low voltage drive power transistor comprises a power MOSFET. A power MOSFET in that article has a structure in which a semiconductor chip (chip) incorporating the power MOSFET is secured on a support substrate made of metal referred to as xe2x80x9cheaderxe2x80x9d; ends of a gate lead and a source lead extending diagonally upward on the header are connected to electrodes (a gate electrode and a source electrode) on the upper surface of the chip with conductive wires; and the upper surface of the header is coated with an encapsulation element made of insulating resin to cover the chip, wires and the ends of the leads.
In such a power MOSFET, the lower surface of the header is exposed to define a radiating surface, and three leads are exposed at one side of said encapsulation element. Two of the leads are the gate and source leads, and the remaining one lead is a drain lead connected to the header. Aluminum is used for the wire connected to the source electrode, and a connection structure having two wires is used to accommodate an increased amount of current.
Further, xe2x80x9ca power MOSFET for power managementxe2x80x9d is described in pp. 19-20 of xe2x80x9cGainxe2x80x9d issued on Sep. 2, 1996 by Semiconductor Division, Hitachi, Ltd. This power MOSFET is described as being primarily used for chargers of portable telephones, video cameras and the like and for power management during the charging and discharging of lithium ion secondary batteries such as power supplies of OA apparatuses and notebook type personal computers.
Furthermore, Japanese Patent Laid-Open No. 307103/1997 (Japanese Patent Application No. 120211/1996) discloses a technique for a composite power MOSFET incorporating a negative voltage protection circuit for preventing any breakdown of the element attributable to a negative voltage applied to the drain.
As described in xe2x80x9cHybrid Packaging Techniquexe2x80x9d issued on May 15, 1988 by Industrial Research Institute, page 25, power transistors are widely used in power supplies for driving motors to operate devices in various parts of an automobile. A hydraulic pump system driven by an electric motor and power steering driven by an electric motor itself are described in xe2x80x9cElectronic Systems of Automobilesxe2x80x9d issued on Aug. 5, 1992 by Rikogakusha, pp. 110-112.
For example, a power MOSFET is used by incorporating it in a rectifier circuit of a power supply of an OA apparatus. While rectifier circuits have conventionally employed diodes, power MOSFETs have recently come into use because of their low on resistance.
The reduced on resistance has resulted in a trend toward power MOSFETs having higher output. Further, the progress of fine processing techniques in the manufacture of semiconductor devices has resulted in power MOSFETs having higher characteristics and, for example, MOSFETs having an on resistance of about 0.34 mxcexa9 (when they are in the form of semiconductor chips) have been developed.
The inventors have developed this time a semiconductor device (resin-encapsulated semiconductor device) in a configuration of a power MOSFET having an output as high as 500 W (5V, 100 A) and have found that following problems can occur as a result of an examination of conventional structures including configurations of encapsulation elements (packages).
In conventional resin-encapsulated semiconductor devices, wires having large diameters are used to provide high output, and two wires are used. While gold wires are desirable because of their low resistance, aluminum is used because of the high cost of gold. Aluminum is connected to electrodes and leads by means of wire bonding utilizing ultrasonic oscillation (USWB) and is formed to have a maximum diameter of 500 xcexcm. This is the maximum dimension of aluminum wires available on the market which is used here because custom-made parts are expensive.
When aluminum wires having a diameter of about 500 xcexcm or more are used, a wire bonding apparatus utilizing ultrasonic oscillation can damage semiconductor chips formed from fragile semiconductors such as silicon, and it is therefore limited to the use of aluminum wires having a diameter of about 500 xcexcm. Further, aluminum wires having a thickness in the excess of 500 xcexcm are unsuitable for use because they can be cracked or cut when wound around a spool. This problem becomes more serious, the higher the purity of aluminum. Aluminum having high purity is used for wire bonding.
In addition, the output of conventional semiconductor devices in the form of power MOSFETs has been in the range from about 200 to 300 W at the maximum, which is quite small in comparison to 500 W which is achieved this time.
When two aluminum wires having a diameter of 500 xcexcm are used, a great amount of heat is generated at the region of the wires, which can deteriorate resin (epoxy resin) having a glass transition temperature (Tg) in the range from about 155 to 170xc2x0 C.
In consideration to this, the inventors examined increase of the number of wires used. According to a study carried out by the inventors, in conventional power MOSFET encapsulating structures, no consideration is paid on heat radiation from a source lead.
In the field of automobiles, while a compressor for power steering has conventionally been driven by a fan belt, there is a trend toward motor-driven systems (hydraulic pump type electric power steering) to reduce the weight of vehicle bodies and fuel consumption.
Further, systems for driving steering directly without a pump (directly driven electric power steering) have come in use in small cars to achieve a further reduction of weight.
Both of the systems described above employ a high current transistor (semiconductor device). For example, hydraulic pump type electric power steering and directly driven electric power steering require currents of 120 A and 70 A, respectively.
Especially, in Europe where regulations exist to prevent electric wave interference, motors must be of the brushless type, and the maximum torque of directly driven electric power steering is determined by the current which is allowed to flow through the transistor, e.g., MOSFET; incorporated in the driving system for the same. This factor consequently determines the total stroke of volume of the cars in which the steering system can be used.
It is assumed that existing transistors in TO220 type packages is limited to use in cars having total stroke volumes up to about 1500 cc because they can only carry a current of about 75 A.
Furthermore, transistors are incorporated in the engine room in an automobile where they can be subjected to a high temperature and are thus used in a severe environment in terms of temperature. Referring to a value as a result of an experiment by the inventors, when a current of 110 A is applied to two wires having a diameter of 500 xcexcm used in a package having an external configuration of TO220AB to connect a source electrode and a source lead, the temperature around the wires rises to 151.5xc2x0 C. (in an ambient temperature of 80xc2x0 C.).
Under such circumstances, in order to improve heat radiating properties of a transistor, a need arises for semiconductor device packaging in which a header carrying a semiconductor chip is directly secured to a heat sink or the like. In this case, it may not be possible to use the header as an electrode lead terminal. In such a case, leads to serve as a drain, source and gate are required as electrode terminals from a package.
It is an object of the invention to provide a semiconductor device (a low voltage drive power transistor, a power transistor for a high current or the like) having a high output in which no deterioration is caused on the encapsulation element due to the generation of heat.
The above and other object and novel features of the invention will be apparent from the description of the present specification and the accompanying drawings.
Typical aspects of the invention disclosed in this specification can be briefly summarized as follows.
(1) There is provided a semiconductor device comprising:
an encapsulation element (a sealing body) made of insulating resin;
a support substrate made of metal covered at least in a part thereof by the encapsulation element and uncovered by the encapsulation element at a lower surface thereof which is to serve as a first electrode;
a suspended lead contiguous with the support substrate protruding from one side surface of the encapsulation element;
a second electrode lead to serve as a second electrode and a control electrode lead to serve as a control electrode protruding in parallel from the side surface of the encapsulation element;
a semiconductor chip covered by the encapsulation element and having the first electrode on a lower surface thereof and the second electrode and control electrode on an upper surface thereof, the lower surface being secured to the support substrate through a conductive bonding material; and
wires provided in the encapsulation element for establishing electrical connection between the second electrode and second electrode lead and between the control electrode and control electrode lead. The second electrode lead comprises a plurality of leads in parallel with each other which are coupled to one coupling portion in the encapsulation element at the ends thereof. The coupling portion and the second electrode of the semiconductor chip are connected to each other by a plurality of wires in parallel with each other. The control electrode lead and second electrode lead protruding from one side surface of the encapsulation element are bent in the middle thereof to provide a structure for surface mounting. The wires comprise aluminum wires, and the number of the wires connecting the second electrode lead and second electrode is three or more (four). The semiconductor chip comprises any of a power MOSFET, a power bipolar transistor or an IGBT whose electrodes are the first electrode (drain electrode), second electrode (source electrode) and control electrode (gate electrode). For example, it comprises a power MOSFET. The control electrode lead and second electrode lead protruding from one side surface of the encapsulation element may be extended straightly to provide a structure for insertion mounting. While the suspended lead is an unused lead which is cut in the vicinity of the encapsulation element, it may be configured in a structure for surface mounting or insertion mounting to be used as a lead for the first electrode.
Such a semiconductor device is manufactured according to a method as described below.
There is provided a method for manufacturing a semiconductor device, comprising the steps of:
providing a support substrate comprising a sheet of metal patterned and bent in a part to form a step, which forms a first electrode and to which a semiconductor chip is secured and providing a lead frame comprising a suspended lead for supporting the support substrate at both side thereof and second electrode lead and a control electrode lead extending in parallel with the suspended lead;
providing a semiconductor chip having a first electrode on a lower surface thereof and a second electrode and a control electrode on an upper surface thereof;
securing said semiconductor chip to the support substrate at the region of the first electrode thereof through a conductive bonding material;
establishing connection between the second electrode of the semiconductor chip and a wire connection portion of the second electrode lead and between the control electrode of the semiconductor chip and a wire connection portion of the control electrode lead with conductive wires;
molding the semiconductor chip, the connection means and a part of the second electrode lead and the control electrode lead in insulating resin to cover them with an encapsulation element; and
cutting and removing an unnecessary part of the lead frame and forming the leads into a structure for insertion mounting or surface mounting, wherein
the second electrode lead is configured in a wide structure wider than the width of the control electrode lead or is constituted by a plurality of leads coupled at a coupling portion in the encapsulation element;
the semiconductor chip is thereafter secured on to the support substrate; and
connection is thereafter established between the second electrode of the semiconductor chip and the end of the second electrode lead having a wide structure or between the second electrode and the coupling portion with a plurality of wires.
The suspended lead is cut in the vicinity of the encapsulation element or is formed into a structure for surface mounting or insertion mounting which allows itself to be used as a lead for the first electrode. A semiconductor chip having a power MOSFET whose electrodes are constituted by the first electrode, second electrode and control electrode is secured on the support substrate, and the second electrode lead and the second electrode are connected with three or more (e.g., four) conductive wires.
(2) In the configuration according to the first aspect, the second electrode lead constituted by a plurality of leads has a wide structure in which the leads are coupled to each other with a link piece in a region outside the encapsulation element. An inserting portion in the form of a protrusion for insertion mounting is formed at the ends of the leads outside the link piece.
In such a semiconductor device according to the method for manufacture in the first aspect, the second electrode lead is formed by a plurality of leads extending in parallel with each other, and the leads are linked to each other by a linking piece in a region outside said encapsulation element.
(3) There is provided a semiconductor device comprising:
an encapsulation element made of insulating resin;
a support substrate made of metal covered at least in a
part thereof by the encapsulation element and uncovered by the encapsulation element at a lower surface thereof which is to serve as a first electrode;
a suspended lead contiguous with the support substrate protruding from one side surface of the encapsulation element;
a second electrode lead to serve as a second electrode and a control electrode lead to serve as a control electrode protruding in parallel from the one side surface of the encapsulation element;
a semiconductor chip covered by the encapsulation element and having a first electrode on a lower surface thereof and a second electrode and a control electrode on an upper surface thereof, the lower surface being secured to the support substrate through a conductive bonding material; and
wires positioned in the encapsulation element for establishing electrical connection between the second electrode and the second electrode lead and between the control electrode and the control electrode lead, wherein
at least the width of a wire connection portion of the second electrode lead to which wires are connected is greater than the width of a wire connection portion of the control electrode lead. The lead portion of the second electrode lead excluding the wire connection portion has a width equal to or greater than the width of the control electrode lead. When the second electrode lead has a wide structure which is to be bent, one or a plurality of holes for uniform bending are provided in a bent portion of the second electrode lead to bend and shape the lead uniformly. A machine screw mounting hole is provided in a mounting region of the second electrode lead. An inserting portion for insertion mounting is formed to protrude from the end of the lead to provide a structure that also allows insertion mounting.
In such a semiconductor device according to the method for manufacture in the first aspect, the second electrode lead of the lead frame is formed such that at least the wire connection portion of the second electrode lead has a width greater than the width of the wire connection portion of the control electrode lead. The second electrode lead is formed wider than the width of the control electrode lead, and the second electrode lead used has one or a plurality of holes for uniform bending at a bent region thereof.
(4) There is provided a semiconductor device comprising:
an encapsulation element made of insulating resin;
a support substrate made of metal covered at least in a
part thereof by the encapsulation element and uncovered by the encapsulation element at a lower surface thereof which is to serve as a first electrode;
a second electrode lead to serve as a second electrode and a control electrode lead to serve as a control electrode protruding in parallel from the one side surface of the encapsulation element;
a semiconductor chip covered by the encapsulation element and having a first electrode on a lower surface thereof and a second electrode and a control electrode on an upper surface thereof, the lower surface being secured to the support substrate through a conductive bonding material; and
wires positioned in the encapsulation element for establishing electrical connection between the second electrode and the second electrode lead and between the control electrode and the control electrode lead, wherein
the second electrode lead has a structure in which the width of a wire connection portion thereof lead to which wires are connected is greater than the width of a wire connection portion of the control electrode lead and in which a plurality of leads extend from the wire connection portion in parallel with each other. Other parts are in the same configuration as in the first aspect.
Such a semiconductor device is manufactured according to the method described below.
There is provided a method for manufacturing a semiconductor device, comprising the steps of:
providing a support substrate comprising a sheet of metal patterned and bent in a part to form a step, which forms a first electrode and to which a semiconductor chip is secured and providing a lead frame comprising a second electrode lead and a control electrode lead extending in parallel toward one end face of the support substrate and a suspended lead for supporting the support substrate at the end thereof on both sides of the support substrate intersecting with one end face thereof;
providing a semiconductor chip having a first electrode on a lower surface thereof and a second electrode and a control electrode on an upper surface thereof;
securing the semiconductor chip to the support substrate at the region of the first electrode thereof through a conductive bonding material;
establishing connection between the second electrode of the semiconductor chip and the second electrode lead and between the control electrode and the control electrode lead with conductive wires;
molding the semiconductor chip, the connection means and a part of the second electrode lead and the control electrode lead in insulating resin to cover them with an encapsulation element; and
cutting and removing an unnecessary part of the lead frame and forming the leads into a structure for insertion mounting or surface mounting, wherein
the second electrode lead is configured in a wide structure wider than the width of the control electrode lead or is constituted by a lead which is wider in a wire connection portion thereof than a wire connection portion of the control electrode lead or by a plurality of leads extending from the wire connection portion;
the semiconductor chip is thereafter secured on to the support substrate; and
connection is thereafter established between the second electrode of the semiconductor chip and the end of the second electrode lead having a wide structure or between the second electrode and the coupling portion with a plurality of wires.
(5) In the configuration according to the first or fourth aspect, the coupling portion or wire connection portion is formed by a plurality of conductor portions each of which is electrically separated, and at least one lead extends from each of the conductor portions. Other parts are in the same configuration as in the first aspect.
Such a semiconductor device utilizes a lead frame as described below. The wire connection portion is formed by a plurality of conductor portions each of which is electrically separated, and each of the conductor portions is formed such that it is connected to any of the leads.
(6) There is provided a semiconductor device comprising:
an encapsulation element made of insulating resin;
a support substrate made of metal covered at least in a
part thereof by the encapsulation element and uncovered by the encapsulation element at a lower surface thereof which is to serve as a first electrode;
a second electrode lead to serve as a second electrode and a control electrode lead to serve as a control electrode protruding in parallel from the one side surface of the encapsulation element;
a semiconductor chip covered by the encapsulation element and having a first electrode on a lower surface thereof and a second electrode and a control electrode on an upper surface thereof, the lower surface being secured to the support substrate through a conductive bonding material; and
wires positioned in the encapsulation element for establishing electrical connection between the second electrode and the second electrode lead and between the control electrode and the control electrode lead, wherein
the width of a wire connection portion of the second electrode lead to which wires are connected is greater than the width of a wire connection portion of the control electrode lead. The width of the second electrode lead is equal to or greater than the width of the control electrode lead. Other parts are in the same configuration as that in the first aspect.
(7) In the configuration according to any of the first through sixth aspects, the end of the coupling portion or wire connection portion of the second electrode lead and the control electrode lead is exposed or protrudes from a side of the encapsulation element. In this example, during the manufacture of the semiconductor device, the end of the coupling portion or wire connection portion of the second electrode lead and the control electrode lead is formed such that it is exposed or protrudes from a side of the encapsulation element.
(8) In the configuration according to any of the first through seventh aspects, the intervals between the leads including the second electrode lead and control electrode lead are constant.
(9) In the configuration according to any of the first through seventh aspects, the intervals between the leads including the second electrode lead and control electrode lead are different at least in a part.
(10) In the configuration according to any of the first through ninth aspects, the second electrode lead is located in the center or close to the center.
(11) In the configuration according to any of the first through tenth aspects, the position of the leads as a whole is biased toward one side of the encapsulation element.
(12) In the configuration according to any of the first through eleventh aspects, a mounting hole is provided in a region of the support substrate that protrudes from the encapsulation element.
(13) In the configuration according to any of the first through eleventh aspects, the region of the support substrate protruding from the encapsulation element is on the order of several millimeters.
According to the first aspect, (a) the heat transfer effect is improved because the second electrode lead is constituted by two leads in parallel with each other.
(b) Since the leads apart from each other are connected to one coupling portion inside, the coupling portion is long enough to allow three or more wires, i.e., four wires to be connected thereto. As a result, the amount of current that flows through one wire is smaller than that in a conventional two line configuration. This makes it possible to suppress the amount of heat generated even at a high source-drain current sufficiently below the glass transition temperature of the resin that constitutes the encapsulation element, thereby preventing the deterioration of the resin. When the source electrode and the source lead are connected by four aluminum wires (having a diameter of 500 xcexcm and a length of 6.0 mm), power loss is on the order of 2.3 W against power of 500 W (5 V, 100 A), which prevents the deterioration of resin.
(c) Heat at the surface of the semiconductor chip is transferred through the four wires and the source lead that provides a high heat transfer effect to a printed circuit board, which allows a stable operation of the semiconductor device.
(d) The control electrode lead and second electrode lead can be straightly extended to provide a structure for insertion mounting. Further, while the suspended lead is cut in the vicinity of the encapsulation element to be an unused lead, it may be formed into a structure for surface mounting and insertion mounting to be used as a lead for the first electrode.
According to the second aspect, in addition to the effects of the first aspect, (a) even when two leads are used, they will be in a wide structure in which they are linked to each other by a linking piece in regions outside the encapsulation element and, as a result, the heat transfer effect is improved to improve the effect of heat radiation at the source electrode.
(b) Since an inserting portion for insertion mounting is provided at the ends of the leads outside the region of the linking piece, the use of the inserting portion allows insertion mounting to provide a type that accommodate both of surface mounting and insertion mounting.
According to the third aspect, in addition to the effect of the first aspect, (a) since the single second electrode lead is wide enough, the heat transfer effect is further improved to contribute to a stable operation of a power MOSFET.
(b) During the manufacture of the semiconductor device, the second electrode lead having a wide structure on the lead frame is formed with a hole for uniform bending to allow it to be bent and shaped uniformly, and the width of each bent portion is equal to or smaller than the width of the control electrode lead. This improves lead shapability and yield.
(c) Since the mounting portion of the second electrode lead can be secured to a printed circuit board with a machine screw using the machine screw mounting portion, the lead can be secured with increased strength and can be directly secured to a printed circuit board. This improves the heat transfer effect and contributes to a stable operation of a power MOSFET.
(d) An insertion portion in the form of a protrusion is formed at the end of the lead to allow insertion mounting, which allows it to accommodate both of surface mounting and insertion mounting.
According to the fourth aspect, four thick wires (having a diameter of 500 xcexcm) can be connected to the wire connection portion of the second electrode lead as in the configuration according to the first aspect even in a structure in which the support substrate is not supported by a suspended lead. This makes it possible to suppress the amount of heat generated at the wires and to prevent damage attributable to heat at the encapsulation element. Further, since the second electrode lead is constituted by a plurality of leads, it is possible to improve the effect of radiating heat through the lead to the outside of the encapsulation element, thereby allowing a stable operation of the semiconductor device to be maintained.
According to the fifth aspect, the suppression of thermal damage to the encapsulation element through the use of four wires having a diameter of 500 xcexcm and the stable operation of the semiconductor device through thermal diffusion at the plurality of leads can be achieved as in the first aspect even in a structure in which the coupling portion and wire connection portion are separated.
According to the sixth aspect, since four wires having a diameter of 500 xcexcm can be connected to the wire connection portion of the second electrode lead, the generation of heat can be suppressed to suppress thermal damage to the encapsulation element. Further, in the case of a wide lead, since heat can be effectively transferred through the lead, it is possible to improve radiation characteristics and to achieve a stable operation of the semiconductor device.
According to the seventh aspect, in addition to the effects of the configurations of the first through sixth aspects, since the end of the coupling portion or wire connection portion of the second electrode lead and the control electrode lead is exposed or protrudes from a side of the encapsulation element, the width of the coupling portion or wire connection portion of the second electrode lead can be increased to improve flexibility of wire bonding or to increase the number of wires connected thereto.
According to the eighth aspect, in addition to the effects of the configuration of any of the first through seventh aspects, since the intervals between the leads are constant, it is easy to provide a product that complies relevant specifications.
According to the ninth aspect, in addition to the effects of the configuration of any of the first through seventh aspects, since there is provided a configuration in which the intervals between the leads are different at least in a part, it is easy to provide a product that complies relevant specifications.
According to the tenth aspect, in addition to the effects of the configuration of any of the first through ninth aspects, since the second electrode lead is positioned in the center or close to the center, the length of the wires connected to the wire connection portion of the second electrode lead can be reduced to provide an effect of suppressing the generation of heat further through a reduction of resistance.
According to the eleventh aspect, in addition to the effects of the configuration of any of the first through tenth aspects, since the position of the leads as a whole is biased toward one side of the encapsulation element, the position of the encapsulation element can be biased during the mounting of the semiconductor device.
According to the twelfth aspect, in addition to the effects of the configuration of any of the first through eleventh aspects, the support substrate can be secured in tight contact with a predetermined position with a machine screw or the like using a mounting hole provided on the support substrate. This allows radiation of heat through the support substrate. In a structure in which a radiation fin is secured to the support substrate, radiation of heat from the radiation fin can be effectively achieved.
According to the thirteenth aspect, in addition to the effects of the configuration of any of the first through eleventh aspects, it is possible to provide a product in compliance with specifications such as TO-263AA and TO-263AB in which the support substrate does not protrude from the encapsulation element in a large amount.